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pubmed:abstractText |
The major ion formed in Negative Ion Chemical Ionization Mass Spectrometry of Adenine, Guanine, Cytosine, Uracil and Thymine is the dehydrogenated anion. The CURES EC procedure for optimizing Austin Model-1 Multiconfigurational Configuration Interaction semi-empirical calculations is applied to the electron affinities of the corresponding dehydrogenated bases and N-H bond dissociation energies. These calculated values will be compared with literature values of the gas phase acidities of the purines and pyrimidines. The N-H bond dissociation energies are about 3.95 eV for Guanine, Adenine, and Thymine and 4.08 eV for Cytosine and Uracil. The electron affinities of the radicals are AMinH = 3.50 eV, GMinH = 3.46 eV, CMinH = 3.38 eV, UMinH = 3.48 eV, TMinH = 3.46 eV.
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